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sprinkler one shot timer

Discussion in 'Electronic Basics' started by emmett, Sep 25, 2007.

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  1. emmett

    emmett Guest

    Hi again group. Have a friend that has coons and possums that are
    messing with his swimming pool. He set up a motion sensor to turn a
    110v sprinkler valve on, and wants it to stay on for a minute or so,
    but the water keeps on "falsing" the sensor. I am trying to come up
    with a simple timer delay that would be set off by the motion sensor
    and would then be in charge of turning the sprinkler valve off after a
    minute or so regardless of motion input. Kind of a one shot mode. I am
    having a mental block with the 110v though as to how to interface that
    with a timer. Am I trying to complicate this? Don't know what the
    specifics are as to motion sensor sensitivity etc. Any suggestions?
    Thanks much !! Wayne
  2. JeffM

    JeffM Guest

    Well, you HAVE that.
    What you're doing is *not dealing with THE PROBLEM*.

    If *motion* AFTER shutdown is the problem,
    you need a **deadband**
    where you disable the trigger until things are still again.
    This requires a *second* timer which trips at the OFF point of the
  3. Guest

    Try putting the sensor out of view of the water...
  4. emmett

    emmett Guest

    Very true on both fronts I realize it needs a timer to turn the water
    on then another
    way of turning the water off for 30 seconds or so. I'm stimyed as to
    how though. I did tell him to try a different lens on the MS like
    sunglasses or aiming it different I'll have him try that first before
    I build a 556 timer board if he feels it is that important Again for
    your time and expertize I am truly grateful I'll be back. Wayne
  5. Jamie

    Jamie Guest

    Use a Timer relay with 2 sets of contacts for the trip cycle.
    A delay off type would be good. One set of contacts will lock it
    on, and the other set of contacts will disable the sensor. Many
    timer relays will reset it's timer if the input retriggers and thus
    it may not expire.
    And for the sensor, you should have a time on delay power source that
    was interrupted from the first timer to disable it. The reason for this
    is, when the main timer expires and turns it self off. This would then
    reconnect the sensor. If water is still in the air, you'll get a false
    start. Using a delay on timer for a power source to run the sensor will
    fix that.
    SO basically, first timer is a Delay OFF type using one set of it's
    own contacts lock on the input signal. the other set of contacts will
    disconnect the power to the Time on delay relay for the sensor..
    When first relay expires. it'll turn on the delay on relay for the
    sensor. mean while, water in the air should be clearing.
    when the delay on sensor expires., the contacts will then close to
    allow sensor activity once again.

    You can actually do all of this with a 556 timer, (dual 555).
    the first timer will be the delay on for the sensor, the Reset line
    of this timer will be controlled from the output side of the second
    timer etc...
  6. ehsjr

    ehsjr Guest

    Simple. What you really need to do is keep the motion
    sensor from being set off by the water from the sprinkler
    system. Use a relay to interrupt power to the sensor,
    or output from the sensor, when the sprinkler is on.
    The drop out of the relay is delayed by a capacitor, so
    the water will finish falling befor the sensor is
    turnde back on.

    The relay will be driven by a transistor, which will
    be held in the on state for a few seconds after the
    sprinkler turns off. I'll draw an NPN circuit as an
    example, which takes a plus 12 from the sprinkler
    when the sprinkler is on, to turn the relay on. (When
    the relay is on, the sensor is interrupted.)

    + 12 ----------+---[Rly]---+
    | |
    Sprinkler /c
    Plus>---+---[1K]---+-----| NPN
    | | \e
    [10K] [470uF] |
    | | |
    Gnd ----+----------+-------+

    In effect, the transistor amplifies the capacitance,
    delaying the dropout *much* longer than if you simply
    placed the cap in parallel with the relay coil. The
    delay will depend on the transistor gain and relay
    coil resistance, but should be a few seconds. You
    can change that to a few minutes, if you want, by
    using a darlington transistor and increasing the 10K
    to 1meg, or make it variable by using a 1meg pot
    with the darlington.

  7. neon


    Oct 21, 2006
    Look up LM555 use it as a oneshot input 2 that will run once untill next transition and i don't think you got 110 volts springler system there is probably 24 v ac transformer in between. for false triggering use another LM555 in series to provide a dead band of time. And use the 24v volts tranformer as a power souce. too complicated ask for more help.
  8. zhafran

    zhafran Guest

    Sorry to interrupt. May I know what is indicated by that symbol just
    below the relay (Rly) in the circuit diagram shown
  9. emmett

    emmett Guest

  10. zhafran

    zhafran Guest

    ahh yes.exactly.thanks
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